The technology of mounting a fuel cell in vehicles, for example, is being implemented because of its ability to reduce adverse effects on the environment. A desirable voltage or current can be obtained from a fuel cell in the form of a fuel cell stack formed of a combination of a plurality of electric cells. Specifically, a required amount of electric power can be extracted from a fuel cell by supplying fuel gas such as hydrogen to an anode side of the a fuel cell stack and supplying oxidizing gas including oxygen such as air to a cathode side of the fuel cell stack to cause an electrochemical reaction through an electrolytic membrane at an appropriate temperature.
Accordingly, in order to operate a fuel cell system, auxiliary devices for a fuel cell including a pump which supplies fuel gas, an air compressor (ACP) which supplies oxidizing gas, a cooling water circulating pump which controls the temperature of the fuel cell stack and so on, as well as sensors such as a cell monitor which detects the voltage, temperature, and so on of each electric cell forming the fuel cell stack are required. Further, in order to operate the fuel cell system, it is necessary to supply electric power to these auxiliary devices and to consider the timing of supplying of the electric power.
JP 2005-332702 A, for example, discloses a fuel cell diagnostic apparatus which measures resistance of a fuel cell when an ignition switch (IG) is turned ON, and thereafter establishes a ready (READY) state to supply electric power to a motor. Further, WO 03096001 discloses that, when an ignition switch is turned ON, application of power to a heater of a gas sensor is started, and then fuel gas is supplied to generate power.
JP 2004-178998 A discloses a controller of a fuel cell vehicle, in which, when a start switch corresponding to an ignition switch is turned ON, a capacitor switch is closed (ON) and the temperature of a fuel cell and the cell voltage are measured, and, if the measured values are low, electric power is supplied from the fuel cell to an auxiliary device for warming up, and thereafter, a main switch is closed (ON) to supply electric power to a motor.
When a fuel cell system is started, it is necessary to supply electric power to a load such as an auxiliary device for a fuel cell, and so on. Here, the electric power is supplied from a power source other than a fuel cell, i.e. from an electric power storage device such as a low-voltage battery. Therefore, when a capacity of such an electric power storage device such as a secondary battery is small or the electric power storage device is not in a sufficiently charged state, sufficient power supply to the load cannot be achieved at the time of starting the fuel cell system, or the charged state of the electric power storage device at this stage is significantly lowered.
Suppression of standby power is similarly desired in stationary fuel cell systems in which electric power is supplied during a standby state through a power transmission line called grid, for example.
It is therefore necessary to review suppression of power supply to a load at the time of starting a fuel cell system. While JP 2005-332702 and WO 03096001 described above disclose that resistance measurement is performed prior to starting and that power is supplied to a heater for a gas sensor, respectively, neither document describes suppression or reduction or restriction of power supplied from an electric power storage device at the time of starting of the system.
As such, conventionally, review on a working state of an electric power storage device, for example, has not been performed as restriction of power supply to a load at the time of starting a fuel cell system.
One advantage of the present invention is to provide a fuel cell system and a fuel cell system start method which enable suppression of electric power consumed by an electric power storage device at the time of starting the fuel cell system. Another advantage of the present invention is to provide a fuel cell system and a fuel cell system start method which enable suppression of electric power supplied to a load at the time of starting the fuel cell system. The solutions described below contribute to achieving at least one of these advantages.